This invention relates generally to a commutator for an electric motor. In particular, the invention applies to an electric motor designed to drive motor vehicle equipment, such as a window regulator, a sunroof or a seat operation motor.
A commutator conventionally includes a commutator ring having a series of conductive segments around its circumference. The commutator ring is designed to be mounted integrally on a rotor shaft.
An electric motor generally includes a stator frame and a rotor mounted rotatably in the stator frame. The motor also includes windings that are integral with the rotor shaft, and each winding is electrically connected to two diametrically opposed segments of the commutator.
The commutator is generally mounted in a commutator housing that is integral with the stator. The commutator housing includes a housing support having a central opening designed to receive the commutator and to allow the rotor shaft to pass through the housing support. The housing support is made of an insulating material, for example a plastic material.
The commutator housing also includes at least one pair of brushes that are diametrically opposed relative to the commutator and designed to contact segments of the commutator during its rotation with the rotor shaft. The brushes are electrically connected to a supply of electric current.
When the motor is operating, as is known, the brushes are pressed against the commutator segments to successively supply the various windings corresponding to the various pairs of diametrically opposed segments with electric current while the commutator is rotating with the rotor.
Thus, when the motor is running, the brushes are successively in contact with the various rotating commutator segments. When a brush passes from one segment to the next, an electric arc can be generated between the brush and the segment which was previously in electrical contact with the brush. The creation of an electric arc is a known phenomenon when a switch is opened and when an electric current is passing therethrough. In the present case, the electric arc is due to the inductive effect of the winding previously powered by the brush.
The appearance of electric arcs or voltage spikes created between the commutator segments and the brushes can, firstly, damage these elements and, secondly, be a source of spurious signals which can interfere with other equipment of the motor or the vehicle.
Further, standards on radio interference set limits on spurious signal propagation from one piece of equipment to another. Thus, the International Special Committee on Radio Interference (CISPR) or other bodies have defined various classes corresponding to different levels of interference. Depending on the vehicle range, vehicle manufacturers are obliged to comply with one of the various classes.
Conventionally, the electric arc phenomenon can be compensated for by inserting an LC (inductive-capacitive) type circuit that constitutes an interference suppressor filter between the two supply brushes of the commutator housing.
The filter must be implemented on the commutator housing, which complicates production of the commutator housing and generally requires manual intervention by an operator. This increases motor production costs.
Additionally, the LC filter does not make it possible to sufficiently filter out induced spurious signals. As a result, motors fitted with these devices do not meet the highest radioelectric interference standards.
French patent 2,814,868 discloses an electric motor commutator having a simplified interference suppressor device. Discharge circuits are provided on a printed circuit board of an annular shape that are sleeved onto the rotor shaft. Each pair of adjacent commutator segments is thus linked by an RC (resistance-capacitance) circuit of the printed circuit integral with the commutator ring. The discharge circuits make it possible to avoid most electric arc phenomena.
Nevertheless, such an interference suppressor device requires production and mounting of the printed circuit. Further, to operate correctly, it is necessary to provide a presser member to permanently keep the printed circuit lands in contact with the commutator segments.
This prior art solution consequently leads to increased manufacturing costs and creates a risk of incorrect operation due to poor contact.
There is consequently a need for a simplified commutator that makes it possible to achieve a high degree of interference suppression while guaranteeing reliable mounting and operation.